Section 3 review
Physics at atomic scales contains many surprises. According to the quantum theory, light has momentum, just like matter. And matter (such as electrons) can exhibit both wave and particle behavior, just as you learned earlier about light. In quantum physics, the position and momentum of a particle cannot be known simultaneously to high precision. Instead, there is an inherent uncertainty in how well we can know position and momentum (or energy and time). But perhaps the strangest feature of the quantum world is that many of the properties of particles are probabilistic or statistical. You don’t know where an electron is located; you only have probabilities for its being in various locations. Read the text aloud
uncertainty principle, wave function, stimulated emission, laser, spontaneous emission

λ= h p
ΔpΔx h 4π
ΔEΔt h 4π

Review problems and questions

  1. In the electron version of the double slit experiment, electrons are detected on a screen and show an interference pattern. Does each individual electron pass through one or the other slit? Read the text aloud Show
  1. Imagine a modification to the electron double slit experiment where you place a detector next to one slit to determine at the location of the slit whether or not each electron passed through that slit. Will the electrons still show an interference pattern on the screen? Read the text aloud Show
  1. One of the best-known paradoxes of quantum physics is called “Schrödinger’s cat.” Imagine a black box that contains a cat and a randomized device that, if triggered, kills the cat. If you wait a while, you won’t know whether the device has triggered and killed the cat, or whether the cat is still alive. If you open up the box and look inside, then you can tell whether the cat is alive or dead. But before you open up the box, according to the concepts of quantum physics, is the cat alive or dead? Read the text aloud Show
  1. Mauro studied quantum physics and has what he thinks is a great idea for a new invention he calls the Earth Tunneler: a tunneling device that will allow him to pass through the solid Earth and show up on the far side. He insists that the concepts of quantum tunneling will allow him to tunnel straight through the Earth. Is his invention a solid idea? Read the text aloud Show
  1. Research the two kinds of laser eye surgery called LASIK and PRK. What wavelengths of lasers are used in them? What is the laser used for? Read the text aloud Show
  1. If you want to know the position of an electron to within the radius of the atom of around 0.5 angstrom (0.5×10−10 m), what is the best precision with which you can know its velocity? Read the text aloud Show

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